A Finnish patent FI-111006 and a U.S. Pat. No. 7,290,405, FIGS. 10 and 11 show a convection arrangement which in practice has proven to be very efficient and well functioning. In the arrangement the pipes of the heaters must be taken through each air channel (nozzle section). The sealing between pipes and channels must be made well. There is a large number of points to be sealed. Making of perforations and sealings causes unnecessary costs and loss related to escape of convection air. The requirement of an efficient convection is the fact that convection air showers meet the glass with great speed. Arrangements according to the FIGS. 7, 8, and 9 of the patent FI-111006 has also been realized but have been found to be much weaker. The reason is the fact that return air cycle interferes with convection air showers and reduces the incidence speed of the air showers coming from the nozzles to the glass. Figure A clarifies the disadvantage of the return flow for convection showers. The capacities of these kind of convection arrangements are approximately 20-40% lower than the methods according to the FIGS. 10 and 11 of the patent FI-111006 depending on the glass type. In addition to that convection air showers should have a heating profile required by each load of glass. Air flowing to the sides also weakens hugely the heating profile. The method according to the patent FI-111006 has thus been found to be the best and the most inexpensive convection arrangement in which method convection air shower areas and exit air areas alternate in relation to the direction of motion of the glass on transversal sectors. The methods according to the FIGS. 1-6 of the patent FI111006 cannot be realized so that they would be technically correct regarding the air flow and reasonable regarding their costs.
One section which has disadvantages in the patents FI111006 and FI20030482 the patent application 2013 0238 relates to the changing of the heaters. It must be performed at the end of the oven because the heaters are long and they are inside casings or pipes. The other disadvantage of the heaters is the fact that the adjusting of the temperature of the oven in a longitudinal direction is difficult, an example is the transverse heaters of the oven described in the patents FI111006 and FI20030482. The third disadvantage is the fact that the mentioned ovens FI 20030482 have long nozzle casings and the oven FI111006 has long pipes for the heaters. The control of their thermal expansion is difficult in relation to other structures, especially in relation to blowing units located in stationary points. Sealings in the thermal expansion points are difficult to realize and escape of the convection air causes loss of power and energy loss.
Efficiency of the convection can be increased, the temperature profile can be improved, the loss of convection air can be reduced and costs can be cut when one acts in the innovative way described in the following: